Do you know who / whom she is going to marry ?
The usage of who and whom has been already explained on SE, going by that to find which pronoun to use we need to replace he / him in the answer, so accordingly him fits here that means I need To use whom here, but my book says who is fine, I know colloquially it doesn't makes much difference and in modern English we can replace whom with who, but this isn't the cause with my exam for which I am preparing I need to strictly follow the conventional grammar so just want to confirm if its a printing error in my book ? Correct answer should be whom , Right ?